Originální popis anglicky:
ilogb, ilogbf, ilogbl - return an unbiased exponent
Návod, kniha: POSIX Programmer's Manual
#include <math.h>
int ilogb(double
x);
int ilogbf(float
x);
int ilogbl(long double
x);
These functions shall return the exponent part of their argument
x.
Formally, the return value is the integral part of log_r|x| as a signed
integral value, for non-zero
x, where
r is the radix of the
machine's floating-point arithmetic, which is the value of FLT_RADIX defined
in
<float.h>.
An application wishing to check for error situations should set
errno to
zero and call
feclearexcept(FE_ALL_EXCEPT) before calling these
functions. On return, if
errno is non-zero or
fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is
non-zero, an error has occurred.
Upon successful completion, these functions shall return the exponent part of
x as a signed integer value. They are equivalent to calling the
corresponding
logb() function and casting the returned value to type
int.
If
x is 0, a domain error shall occur, and the value FP_ILOGB0
shall be returned.
If
x is ±Inf, a domain error shall occur, and the value
{INT_MAX} shall be returned.
If
x is a NaN, a domain error shall occur, and the value
FP_ILOGBNAN shall be returned.
If the correct value is greater than {INT_MAX}, {INT_MAX} shall be returned and
a domain error shall occur.
If the correct value is less than {INT_MIN}, {INT_MIN} shall be returned and a
domain error shall occur.
These functions shall fail if:
- Domain Error
- The x argument is zero, NaN, or ±Inf, or the
correct value is not representable as an integer.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then
errno shall be set to [EDOM]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid
floating-point exception shall be raised.
The following sections are informative.
None.
On error, the expressions (math_errhandling & MATH_ERRNO) and
(math_errhandling & MATH_ERREXCEPT) are independent of each other, but at
least one of them must be non-zero.
The errors come from taking the expected floating-point value and converting it
to
int, which is an invalid operation in
IEEE Std 754-1985 (since overflow, infinity, and NaN are not
representable in a type
int), so should be a domain error.
There are no known implementations that overflow. For overflow to happen,
{INT_MAX} must be less than LDBL_MAX_EXP*
log2(FLT_RADIX) or {INT_MIN}
must be greater than LDBL_MIN_EXP*
log2(FLT_RADIX) if subnormals are
not supported, or {INT_MIN} must be greater than (LDBL_MIN_EXP-LDBL_MANT_DIG)*
log2(FLT_RADIX) if subnormals are supported.
None.
feclearexcept() ,
fetestexcept() ,
logb() ,
scalb()
, the Base Definitions volume of IEEE Std 1003.1-2001, Section
4.18, Treatment of Error Conditions for Mathematical Functions,
<float.h>,
<math.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
